Pulse intercommunication telephone system



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New York, N. Y., a, corporation of Delaware ApplicationAugust 6, 1947, Serial No. 766,583

In France .luly 4, 1946 Section l, Public Law 690, August 8, 1946 Patent expires `uly 4, 1966 Y 2 Claims.

The present invention relates to intercommunication telephone systems.

in known intercommunicating telephone systems there are as many 'lines as telephone 'substations and, from any substation it is possible to call directly any other y'sr-ibstation lay-selecting .the corresponding line. Such installations have therefore even for a relatively small number of substations, a large number of lines and costly wiring, and it is often preferred when the number of substations exceeds for instance ten, Ato install a private branch exchange, manual vor automatic, where all the substation's are connected by one pair of wires.

One object of the present invention is to eliminate the private branch exchange While a simple 'inter-connecting network vis used, connecting vall the substation sets. This result isi-obtained by using a system of pulses for the transmission of the voice current and for signaling.

in an lembodiment all the substation sets are connected to two common lines, one for transmission and one .for reception. From a central point pulses foi very short duration are sent on the first line, these pulses in the iirst place lconnect the receivers of the substations to the 're- Vceiving line at instants that are respectively characterizing one of the substations, in the second place they make it possible for a calling subst'a tion to send voice amplitude modulated pulses at instants characterizing the `lcalled substation. These lpulses arrive therefore fat-the calledsubscriber at the instants when the `receiver' of the telephone set is connected to the receiving line, and the voice of the calling subscriber regen* erated in the receiver. /On' the other hand, the system -must be such that it is possible to Adeterminewhether the line called is -busy `or not, to call this line and to avoid interfering with a connection already established.

It is known to reproduce a periodical current representing, for instance, the voice bymeans of a series of pulses transmitted at 'regular intervals the amplitude of which varies according to the iiuctuations of the current to be transmitted The minimum number of -pulses per second `is from two to three times the maximum frequency which it is desired to transmit, for the voice, for instance, it will be necessary to use about 8,000 pulses per second. If, however, these pulses are very short, for example, of a duration of one microsecond, it is possible to place between two consecutive pulses used for a given telephone channel another series of impulses used for other channels, in this way it is possible forv afgiven number of substations,V all of them connected .to the same line, to communicate simultaneously two by two. But, in order to avoid any cross-talk between two conversations, it is necessary tocannect effectively the receiver of a telephone substation only at the instant wheny the 'pulses lintended for this receiver .are received. l

The invention will be described in vrelation to an embodiment and to the drawings -in which- Figure l shows a schematic incorporating features of the invention.

Figure 2 is an'other schematic.

Figures 3, 4, 5 and 6 are simplified .schematics of the installation shownfonFigure lZat diierent stages of the connection .Referring to Figure-LG is the pulse-generator, giving, for instance 8,000 pulses per secondwhich 'are transmitted on the transmitting line At substation A, a retardation line LRA delays these pulses for a fixed length of time tA, which characterizes substation A. The delayed pulseseffectively lconnect the receiver RA tothe receiving line R at instants ta, computed from the time pulses are transmitted by G.

In l'a similar way, receiver .Re is effectively connected to line R only at instants-ts. .In order that subs-tation Amay be able to speak gto .substation B, itis necessary that adjust delay of a variable retardation line te, Thisline is icorr-- nected to the transmitter Ms, in such away that lthe pulses received .from G, amplitude modulated by transmitter Mn land sent .back on thel line T, arrive V'on the receiver vRe through a :directional device D, and eventually an amplifier E andthe line R, at instants when this receiver .Re is ef- .fectively connected to line R.

In the same mannen, substation B must adjust its retardation vline LRE at :delay its corresponding to .substation A, such a way that ythe pulses modulated by transmitter MB arrive at instants 'tu at receiver RA. It clear that the time of propagation along lines VT and R mustlbetaken finto account, if necessary, in the adjustmentv of, the retardation lines.

Figureashows amore Idetailed schematic com -prising 'auxiliary devices such as busygtests ,g:cali, non-interference of :a third substation maconnection.l

To this effect, every substation is characterized by a given time delay t computed from the time of transmission of one pulse for the busy tests and for calling and by a time delay t-l-At for conversation. 'Ihe additional delay At at each substation are respectively produced by two additional Y v, A 3 retardation lines Zr and lr placed into the circuit at the time of conversation by means of contact of I and I'. l

For calling every substation has an interrupter K which modulates in amplitude the pulses received from the line T at a frequency which is, for example, of the order of 1,000 to 2,000 cycles per second. These modulated pulses may produce in a receiver R a sound which can be heard at a distance.

When A wants to talk with B, he adjusts LRA to the delay te and closes contact h2. Its receiver RA is thus effectively connected to the line R at times tB thru LRA T, D, and E.

In case B is busy, contact 1154 is closed and LRB' transmits on line R thru D and E pulses at instants ts which are received by A. Figure 3 shows the circuit at the stage.

In case when B is not busy, A operates interrupter KA which modulates in amplitude the pulses delayed by LRA and this produces in receiver RB a loud tone. Figure 4 shows the circuits at this stage.

As soon as B replies, contact In* is closed. Pulses are transmitted at instant tB and this places B in busy condition.

Figure 5 shows the circuits at this stage.

B then adjusts its retardation line LRB to delay tn and calls A with interrupter KB. Since RA (or Re) has received the call and since A (or B) is at its substation telephone set, contacts IA and IA (or IB and IB) open, contacts IAZ (or 1132) also open. Contact Is3 is then closed. The two substation sets are at this time in condition for conversation, transmission being made in direction A-B at times tB-I-Atand in direction B-A at times tA-l-At. Figure 6 shows the circuit at this stage.

No other .substation set can receive signals at this-time. However, it might send signals if, being already connected to a 4th substation set, it changes the adjustment of its retardation line LR. It is possible to prevent this by providing a locking device (not shown).

Although the invention has been described with regard to a particular embodiment, it is clear that it is in no way limited to this embodiment.

In particular, it is possible to simplify the arrangement shown. It is possible, in fact, to suppress the iiXed retardation lines LR and lr -byadjusting the Ytwo substation sets which are to be connected so that they operate at the same characteristic instants, for example, that of the called subscriber. In this case, the normal value given to retardation line LR of each line will be that giving a delay equal to the length of time which characterizes this substation set, this value being changed only during a call or for a conversation originating in this substation set, to adjust it to the normal value of the delay of the called substation set. Y

According to another embodiment of the invention, it is possible to provide only one common line for all the substation sets. A sense is given to the primary pulses generated by the pulse generator, for instance, positive in a given direction, and negative for the ampliiied pulses used in the other direction. `In this case, rectiiers will be used to direct these pulses to the proper apparatus.

The connection of the receivers with the lines may be made either by vacuum tubes or by other variable resistance devices, such as, dry rectiers. The lines may be made of two screened parallel Wires, or of a coaxial pair.

It is also possible to provide a call register with each substation or at a central point, in thiscase, there must be provided with the call register retardation lines, respectively adjusted to the characteristic delay of each substation set.

What is claimed is:

1. In an intercommunication telephone system, a plurality of subscribers sets, transmission means connecting all of said sets, means for applying pulses of very short duration to said transmission means, a first receiving means at each of "Y saidsets connected to said transmission means for receiving said pulses, a second receiving means at each of said sets connected to said transmission means, means controlled by said first receiving means at each set for rendering said second receiving means at each of said sets responsive to said pulses for predetermined characteristic times, and a third receiving means at each set for'receiving said pulses from said transmission means including modulating means for modulating with intelligence the pulses thus received, variable time delay means for delivering said modulated pulses to said transmission meansl additional time delay means for each of said rst receiving means and said third receiving means; one of said delay means serially connecting corresponding of said rst receiving means and corresponding of said sets, and the other of said delay means serially connecting corresponding of said third receiving means and corresponding of said sets, and means to render said delay means inoperative when said sets are not in conversation condition.

2. In an intercommunication telephone system, a plurality of subscribers sets, two common lines connecting all of said subscribers sets, one of said lines being employed for transmission, the other one of said lines being employed for reception, means for applying to said transmission line, pulses of a very short duration, each of said subscribers sets responsive to said pulses at predetermined characteristic times, means responsive to said pulses connecting said subscribers sets receivers with said receiving line at instants corresponding to the predetermined times which characterize each of said subscribers sets respectively, whereby a calling subscribers set voicemodulates said pulses at the times which characterize thev called subscribers set, and variable means at the called subscribers set to delay said pulses a predetermined characteristic time corresponding to said calling subscribers set.

STANISLAS VAN MIERLO.

e REFERENCES CITED UNITED STATES PATENTS Name Date Schroeder Aug. 20, 1946 Number 

